The present invention relates to the conversion of analog values to real world values, and vice versa. More particularly, the present invention relates to a system and method for directly converting analog current and voltage values to and from real world values, as used within a control system.
Analog input devices and output devices within an automation or other control system typically use 4-20 mA signals as their output and input, respectively. These signals must be converted into/from (depending on whether the device is an input or output device) a digital signal as used by controllers, typically programmable logic controllers (PLCs) and other digital devices. For an input signal, in addition to the conversion from an analog signal (i.e., 4-20 mA) to a digital signal, the signals must also be converted to a real world values so that the device in question has some meaningful representation of what is actually happening within the control environment, such as degrees Likewise, when meaningful representations are used within controllers or other digital devices, these representations must be converted to an analog signal which can be used by the output device.
In the context of input devices and the signals therefrom, with reference to FIG. 1, one prior system included a multi-channel (multiple signals) input multiplexor 2. In this case, one to N channels of 4-20 mA signals, where N was less than or equal to eight, are shown as input signals 10, 12, 14 to an input multiplexor 2. The input multiplexor 2 sends a 1-5 volt signal (input mux output signal 20) to an analog to digital (A-D) converter 4, which is capable of converting 0-5 volt signals to a digital output value of 0-32,000 (A-D output signal). Thus, since the input signal 20 to the A-D converter 4 is only a 1-5 volt value, the digital output values 22 will only be in the range from 6400-32000. However, to comply with accepted industrial standards, the ultimate digital output value 24 needed would be a number between 0-32000 decimal. Thus, the system also included a microprocessor 6, which would include conversion software code 8 running thereon to mathematically convert the A-D converter output value 22 of 6400-32000 to an ultimate output value 24 of 0-32000, and vice versa in the context of output devices. An analog input signal 10, 12, 14 of 4 mA would thus become an ultimate output value 24 of 0. An analog input signal 10, 12, 14 of 12 mA would become an ultimate output value 24 of 16000. Likewise, an analog input signal 10, 12, 14 of 16 mA would become an ultimate output value 24 of 24000, and an analog input signal 10, 12, 14 of 20 mA would become an ultimate output value 24 of 32000.
Digital values converted by the conversion software code 8 are in sixteen bit format. Since the conversion code makes use of multiply operations, the conversion process is long when using low cost eight or sixteen bit microprocessors. In this type of prior system, the input channels 10, 12, 14 would be read in sequential order (channel 1, 2, 3, . . . , N, where N is less than or equal to 8), then repeat. There is a requirement that the conversion code 8 running in the microprocessor 6 take no more time to perform the conversion calculations than it takes to obtain the next reading for the next channel, 10, 12, 14 from the A-D converter 4. Hence, for a low-cost systems, there is a limitation with the process time of the conversion code 8 in conjunction with the microprocessor 6. In addition, the ultimate output values 24 are difficult for a process engineer to read and interpret since this value is not in an easily understandable format (i.e., an analog input signal 10, 12, 14 of 12 mA would become an ultimate output value 24 of 16000, instead of say 12000). These limitations of the above system shown in FIG. 1 used for input devices, is also true of the prior system for output devices shown in FIG. 2. The prior system shown in FIG. 2 works in the same fashion as the system shown in FIG. 1, only reversed.
The present invention is provided to solve these and other problems.
A first system is provided having a plurality of analog input signals for a plurality of analog input devices. Each analog input signal has an analog input signal value. The first system converts each analog input signal value to an ultimate digital input value. The first system has an input converter for converting each analog input signal to a digital input signal having a digital input value. The digital input value directly corresponds to the analog input signal value. The first system also has a conveying means for conveying the analog input signal value as an ultimate digital input value without performing any additional conversion.
A second system is also provided having a plurality of analog output signals for a plurality of analog output devices. Each analog output signal has an analog output signal value, and each analog output signal value is converted from an initial digital output signal value. The second system has a receiving and conveying means for receiving the initial digital output signal value, and for conveying the initial digital output signal value as a conveyed digital output signal value, without performing any conversion. The second system also has an output converter for converting the conveyed digital output signal value into the analog output signal value. The analog output signal value directly corresponds to the conveyed digital output signal value.